Tarnish resistant alloy

ABSTRACT

A tarnish-resistant alloy, especially useful in the presence of sulfur and sulfur-containing environments, comprising 39 to 47 weight percent gold, 9 to 12 weight percent palladium, and the balance silver and copper wherein the silver-to-copper weight ratio is from 1:1 to 1.5:1.

United States Patent 91 Tuccillo et al.

[ 1 Oct. 23, 1973 TARNISH RESISTANT ALLOY [73] Assignee: Pennwalt Corporation,Philadelphia,

22 Filed: May 19, 1969 21 Appl.No.: 825,943

{52] US. Cl. 75/134 C, 75/165 [51] Int. Cl C22c 5/00 [58] Field of Search 75/134 R, 134 N, 75/165, 134 C [56] References Cited UNITED STATES PATENTS 1,339,009 5/1920 Van Allen 75/165 1,987,451 1/1935 Taylor 75/165 X 1,987,452 1/1935 Taylor 75/165 2,050,040 8/1936 Coleman et al. 75/165 2,050,077 8/1936 Wise 75/165 X 2,200,050. 5/1940 Auwarter et al 75/165 2,216,495 10/1940 Loebich 75/165 2,270,594 1/1942 Leuser 75/165 X 2,274,863 3/1942 Leuser 75/165 2,298,261 10/1942 Mlttendorf et al. 75/165 X 2,304,416 12/1942 Leuser 75/165 2,572,377 10/1951 OMorrow 75/165 FOREIGN PATENTS OR APPLICATIONS 211,340 11/1940 Switzerland 75/165 219,711 6/1942 Switzerland....

222,301 10/1942 Switzerland....

508,669 7/1939 Great Britain 620,031 3/1949 Great Britain 75/165 Primary Examiner-L. Dewayne Rutledge Assistant ExaminerE. L. Weise Attorneystanley Litz and Carl A. Hechmer, Jr

[ 57] ABSTRACT copper wherein the silver-to-copper weight ratio is from 1:1 to 15:1.

2 Claims, No Drawings Metal constituent range of about 65 to 75% gold and platinum group metals.

The good sulfur tarnish-resistance of the new alloy is demonstrated by the following examples in which the new alloy (specimens H to K) is compared to a high precious metal-content alloy (specimen G) as well as to alloys prepared in accordance with U.S. Pat. No. 3,424,577 and alloys wherein the proportions of constituents are outside of the critical, claimed ranges (specimens A to F). The term other metals refers to minor amounts of the non-essential constituents mentioned above.

in alloy, wt. percent B C D E F G H I J K Gold. 46 39 46 40 39 42 60 42 42 40 39 Palladium 6 4 6 7 8 9 4 9 12 10 9 SilVer 19 33. 5 18 28 31 29 22 26 26 24 27. 6 Copper 29 21. 5 28 25 18 14 21 18 24 22. 4 Other metals 2 2 2 2 2 2 2 2 2 28, 1969, there is disclosed a non-tarnishing alloy which consists of 50 to 60% total of silver and copper, 3 to 6% palladium, and the balance gold. (All proportions of constituents of the alloys discussed herein are presented in percent by weight of the total alloy composition). We have discovered that an inherent deficiency in the alloy described by said patent is its inability to resist serious tarnishing in a sulfur-containing environment. Tarnishing is herein defined as the microscopic (100 X magnification) detectable discoloration of an alloy caused by a thin adherent layer of reaction products, such as oxide and sulfides, induced by chemical reaction between the metal constituents and substances in the environment in which it is placed. Eventually, such discoloration becomes noticeable to the human eye and detracts from the beauty and natural appearance of the alloy. Thus, jewelry made from such a tarnish-prone alloy will eventually present an unattractive appearance when subjected to a somewhat moist atmosphere were sulfur oxides content is higher than normally encountered. More importantly, a tarnish-prone alloy used in the dental field is particularly subject to sulfur blemishment, especially when the wearer of the dental appliance enjoys a diet of sulfurrich foods such as fish products.

We have now discovered an alloy composition that is unexpectedly very resistant to tarnishing in the presence of sulfur and sulfur containing compounds in the environments as set forth above, said alloy comprising 39 to 47% gold, 9 to 12% palladium, and the balance silver and copper wherein the silver to copper ratio is from 1:1 to 1.5 :l. Preferably, the gold content is about 40% to 42%, palladium is 9% to about 10%, and the ratio of silver to copper about 1.2:1 to about 1.4: l. The most preferred alloys have a silver-to-copper ratio of about 1.4:1 and a gold content of about 42%. It is essential, however, that the alloy contain at least 9% palladium to achieve the tarnish resistant properties desired. More than 12% palladium, however, is wasteful of this precious metal. In addition, the alloy may contain minor amounts, i.e., up to l or 2%, of other modifying but non-essential metals, such as zinc, nickel, indium, tin, iridium and others and combinations thereof. The tarnish resistance of the alloys embodied in this invention is comparable to the very expensive alloys having high precious metal content, for example, in the The following test procedure is used to determine resistance to tarnishing. A cast specimen of the alloy to be tested is mounted in clear Lucite resin, then wet surface ground through 600 silicon carbide grit and polished with aluminum oxide on a rotating velvet cloth. The tarnish test apparatus consists of a plastic, vertically rotating wheel with eight one-inch diameter holes along its periphery in which the standard metallographically mounted specimens are clamped. The wheel is rotated at one revolution per minute with the lower third of the wheel submerged in anaqueous solution of 5% sodium sulfide, at room temperature. The height of the aqueous solution is adjusted to allow each specimen to be alternately immersed and withdrawn for 15 seconds and 45 seconds per revolution, respectively.

After less than revolutions in the sodium sulfide solution, tarnish-test apparatus described above, the alloy specimens A through F are unacceptably tarnished. The high precious metal-content alloy specimen G shows no incipient tarnish until 700 revolutions in the apparatus are completed. However, the lower cost alloy of this invention also performs remarkably well; specimens H, l, J and K first show incipient tarnish after 700 revolutions. As the tests are continued through a greater number of' revolutions, thevalloy specimens A F show increased tarnish, whereas additional tarnish formation on the alloys of this invention is not significant.

The-foregoing and other tests demonstrate that the alloys embodied herein retain their pleasing colors of yellow, white and combinations thereof even in the:

presence of harmful sulfur compounds.

We claim:

1. An alloy resistant to surfur tarnish when placed in an environment in which said alloy is contacted by sulfur or sulfur-containing compounds, said alloy consisting essentially of 39 to 47 weight percent gold, 9 to 12 weight percent palladium, and the balance silver and copper wherein the silver to copper weight ratio is in the range of 1:1 to 1.5:].

2. An alloy according to claim 1 wherein the gold content is about 40% to 42%, palladium content is 9% to about 10%and the ratio of silver to copper is about 1.221 to about 1.4:1.

nm'mn sums PATENT omen; CERTIFICATE OF CORRECTION Patent No. 5 mud October 23, 1973 Inventor) Io seph I. Tuccillo and Iohn P. Nielsen It is certified that error :ppearsin the above-identified patent and that said Letters Patent are hereby corrected as shown ho low:

Column 1, line 41, "were" should read where Column 2, line 55,- "surfur" should read sulfur Signed and sealed this 5th day ,of Mar'ch 1971+.

(SEAL) Attest:

EDWARD M .FLETCIIEH JR M C MARSHALL DANN Attestmg officer Commissioner of Patents FORM FO-IOSO (IO-9) 

2. An alloy according to claim 1 wherein the gold content is about 40% to 42%, palladium content is 9% to about 10% and the ratio of silver to copper is about 1.2:1 to about 1.4:1. 